C9orf72 and motor neuron disorder: C9ORF72-FTD has recently been identified as a major cause of familial FTD, FTD associated with motor neuron disease and apparently sporadic FTD.2–4 Histopathologically, C9ORF72-FTD has been associated with cellular inclusions containing TAR-DNA-binding protein 43 (TDP-43) subtypes A and B and protein p62.3, 5–7 The pathophysiological mechanisms of C9ORF72-FTD are of particular clinical and neurobiological interest on account of its phenotypic heterogeneity and certain specific phenotypic features.